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Psychology (1,978)
PS295 (14)
Chapter

# PS295 Chapter Ten Summary.docx

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Department
Psychology
Course
PS295
Professor
Roger Buehler
Semester
Winter

Description
PS295 Chapter Ten Summary Analyzing Experimental Data An Intuitive Approach to Analysis  If the IV has an effect on the DV we should find that the means for the experimental conditions differ.  Different group averages would suggest that the IV had an effect; it created differences in the behaviour in various conditions and resulted in systematic variance Error Variance Can Cause Mean Differences  Problem: means of experimental conditions may differ even if the IV does NOT have an effect  Error variance reflects the random influences of variables that remain unidentified in the study  These uncontrolled and unidentified variables lead participants to respond differently whether or not the IV has an effect. Inferential Statistics  If we can estimate how much the means of the conditions are expected to differ even if the IV has no effect, then we can determine whether the difference we observe between the means exceeds this estimate.  We can conclude that the IV has an effect when the difference between the means of the experimental conditions is larger than we expect it to be when that difference is due solely to the effects of error variance. Hypothesis Testing The Null Hypothesis  Researchers use inferential statistics to determine whether observed differences between the means of the experimental conditions are greater than expected on the basis of error variance alone  The null hypothesis states that the IV did not have an effect on the DV and the opposite is experimental hypothesis which states that the IV did have an effect  Rejecting the null hypothesis means that the researcher will conclude that the IV did have an effect and failing to reject the null… means that the researcher will conclude that the IV has no effect.  The researcher will fail to reject the null if analyses show a high probability that the difference between the groups means reflects nothing more than the influence of error variance Type I and Type II Errors  Researcher may make decisions about the null and outcomes may result into four possible outcomes (1) The researcher may correctly reject the null thereby showing a true effect of the IV (2) the research may correctly fail to reject the null concluding that the IV has no effect ..the other two are type I and type II errors..  A type I error occurs when a researcher concludes that the IV has an effect on the DV when in fact the observed difference between the means is actually due to error variance
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